support/scripts: add xorg-release.py script

This script generates a report on the packaging status of X.org
releases in Buildroot. It does so by downloading the list of tarballs
that are part of a given X.org release, and compare that with the
packages that are available in Buildroot.

[Peter: drop .py suffix, make executable]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>